HClO-Activated Near-Infrared Fluorogenic Aza-BODIPY-Bisferrocene Triad with High Turn-on Ratio for In Vivo Biosensing.

Optically monitoring hypochlorous acid (HClO) in living body favors diagnosis and study of inflammatory diseases. However, this has been hampered by limited strategies to develop highly fluorogenic tools in the deep-penetration near-infrared spectrum. Herein, a near-infrared aza-BODIPY-bisferrocene triad Fc2 -CBDP that unexpectedly achieves an exceptionally sensitive and selective fluorescence turn-on (>220-fold) response toward HClO through single-ferrocene oxidation and boron-alkynyl hydrolysis cascade is reported. Mechanism insight shows that Fc2 -CBDP features "enhanced charge transfer"-caused quenching due to intramolecular bisferrocene electronic coupling, which is decoupled in the reaction with HClO. The utility of Fc2 -CBDP for intracellular HClO imaging is evaluated and, more importantly, in vivo high-contrast deep-tissue imaging of lymphatic inflammation and colitis is realized. This work provides new insights into both HClO and ferrocene chemistry, and extends the reach of fluorogenic strategies in the near-infrared biosensing.